An agricultural harvester, such as a combine, is a large machine used to harvest a variety of crops from a field. A combine includes a header at the front of the combine to cut the ripened crop in the field. A feeder housing supporting the header transfers the crop material into the combine for threshing. The threshing and separating assemblies within the combine remove grain from the crop material and transfer the clean grain to a grain tank for temporary holding. Crop material other than grain exits from the rear of the combine and is distributed upon the field. An unloading auger or conveyor transfers the clean grain from the grain tank to a transport vehicle.
Off highway vehicles, such as combine harvesters, currently have a basic engine torque curve to provide a nominal rated power at a power level approximately 14% below the power capability envelope of the engine. This enables the use of a power boost for unloading or a power bulge for additional power to handle gradual increases in a load or to handle slugs or other operational overloads without excessive loss of functional engine speed or the stalling of the engine. Traditional engine torque curves for combines have been developed to use this high level of power bulge above the normal rated power in order to enhance the ability of the power train and threshing system to handle the slugs and transient overloads during the harvesting operation. Such an overload may occur when clumps of moist material suddenly enter the threshing system causing higher, short duration overloads.
Experience has shown that 14% power bulge (from 2,200 rpm rated speed down to 2,000 rpm peak power) provides good slug handling capability and enhanced drivability for the operator.
At the lower power end of the operational spectrum, work vehicles such as combines also spend significant time at very light loads, such as idling or going down hills. In these cases, the high end torque curves that work well for performance, such as slug acceptance, high threshing loads, unloading grain on the go, etc., do not return as good of fuel economy as an engine torque curve optimized for a lower power level operation. In addition, after treatment devices the are used to meet the Environmental Protection Agency's Tier 4 requirements need to operate at temperatures of around 300° Celsius or higher in order to regenerate the after treatment device, and these temperatures are typically not achieved when a high power torque curve equipped engine is operated at light loads. In order to maintain the high temperature, additional fuel is burnt in the exhaust to elevate the temperature of the exhaust, thus exacerbating the fuel consumption problem.
What is needed in the art is a system to modify torque curves dependant upon operational needs.